The present invention relates to cleansing blocks suitable for immersion in toilet tanks. The blocks are formulated to inhibit formation of toilet rings and surface stains.
Various cleansing blocks for use in toilet tanks and other water reservoirs are known. Such cleansing blocks typically contain a surfactant for cleaning, and often fillers, binders, colorants, extrusion aids and perfumes. They are designed to slowly release these materials into the toilet basin each time the toilet is flushed. See e.g. U.S. Pat. No. 5,336,427. The disclosure of this patent, and of all other publications referred to herein, are incorporated by reference as if fully set forth herein.
Such blocks should not include materials which leave undesirable residues in the toilet bowl, which are environmentally unacceptable, or which have unpleasant odors. While blocks having these desired attributes have been created, there are trade-offs between desired characteristics for each formulation. In particular, there is great difficulty in formulating a block that is long lasting, yet which sufficiently inhibits toilet bowl ring and stain formation.
Certain polymers have been added to assist in this regard. See e.g. U.S. Pat. Nos. 4,861,511, 4,899,398, 4,283,300, 4,302,350, and 4,428,872. However, such polymers are relatively costly, can require high concentrations in the toilet bowl in order to be effective, and in some cases can be counterproductive.
For example, in U.S. Pat. No. 4,861,511 a mixture of polyacrylate polymer with substantial amounts of an expensive polymer is stated to be required to achieve adequate results, particularly with respect to iron oxide deposits.
Thus, it can be seen that a need exists for an improved toilet cleansing block.